Internet data usage issues...

We just recently switched to att fiber plan at our home, and I don’t understand how we are going over our usage allowance.  I just pulled up our data usage chart online to find that apparently I’ve already downloaded over 3gb on 7/4/19 - and it’s currently 1030pm on 7/3/19 - can someone with At&t explain to me how I’ve already used over 3gb tomorrow?  I’m beginning to think that my “overages” that I will get charged for may not be so accurate.